media: v4l: async: Fix notifier list entry init

struct v4l2_async_notifier has several list_head members, but only
waiting_list and done_list are initialized. notifier_entry was kept
'zeroed' leading to an uninitialized list_head.
This results in a NULL-pointer dereference if csi2_async_register() fails,
e.g. node for remote endpoint is disabled, and returns -ENOTCONN.
The following calls to v4l2_async_nf_unregister() results in a NULL
pointer dereference.
Add the missing list head initializer.

Fixes: b8ec754a ("media: v4l: async: Set v4l2_device and subdev in async notifier init")
Cc: <stable@vger.kernel.org> # for 6.6 and later
Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>